Method for removing contaminants from a fluid stream

ABSTRACT

A method for removing at least one contaminant from a fluid stream includes filtering the fluid stream with a filtration medium. The filtration medium includes an impregnate. The impregnate includes an organic amine and an inorganic metal salt. The inorganic metal salt includes magnesium oxide, calcium oxide or combinations thereof. The medium has from about 0.1 to about 25% by weight of impregnate. The impregnate contains from about 0.1 to about 5% by weight organic amine, and the organic amine includes aqueous urea, solid urea, melamine or mixtures thereof. The impregnate contains from about 0.1 to about 5% by weight metal salt. The impregnate optionally further includes a surfactant such as polyacrylic acid. In some embodiments, the method includes removing at least two contaminants from the fluid stream.

RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.12/726,746 filed Mar. 18, 2010, which issued as U.S. Pat. No. 8,247,346on Aug. 21, 2012, and which claims the benefit of U.S. ProvisionalPatent Application No. 61/161,202, filed Mar. 18, 2009, the entiredisclosures of each of which are incorporated by reference herein intheir entirety.

TECHNICAL FIELD

The present invention relates generally to compositions and methods forthe removal of compounds having disagreeable odors, toxic properties orcorrosive properties from gaseous streams and more particularly relatesto the use of air filtration media in filter beds.

BACKGROUND OF THE INVENTION

The removal of toxic, corrosive and odorous gases can be accomplished bya number of techniques. These may include wet scrubbing, incineration,and removal via gas-phase air filtration using a variety of dryscrubbing adsorptive, absorptive, and/or chemically impregnated media.As opposed to these other methods, gas-phase air filtration does notrequire the consumption of large quantities water or fuel. Dry-scrubbingmedia can be engineered from a number of common adsorbent materials withor without chemical additives for the control of a broad spectrum ofgases or tailored for specific gases.

In contrast to the reversible process of physical adsorption, chemicaladsorption, also referred to as chemisorption, is the result of chemicalreactions on the surface of the media. This process is specific anddepends on the physical and chemical nature of both the media and thegases to be removed. Some oxidation reactions can occur spontaneously onthe surface of the adsorbent, however, a chemical impregnate is usuallyadded to the media. The impregnate imparts a higher contaminant removalcapacity and can lend some degree of specificity. Although someselectivity is apparent in physical adsorption, it can usually be tracedto purely physical, rather than chemical, properties. In chemisorption,stronger molecular forces are involved, and the process is generallyinstantaneous and irreversible.

Undesirable airborne compounds such as hydrogen sulfide, ammonia andformaldehyde occur in a number of environments, where most are primarilyresponsible for the presence of disagreeable odors or irritating ortoxic gases. Such environments include municipal waste treatmentfacilities, paper mills, petrochemical refining plants, morgues,hospitals, anatomy laboratories, hotel facilities, museums, archives,computer and data storage rooms, and other commercial and industrialfacilities.

These undesirable compounds may be bacterial breakdown products ofhigher organic compounds, or simply byproducts of industrial processes.

Hydrogen sulfide (“H₂S”), a colorless, toxic gas with a characteristicodor of rotten eggs, is produced in coal pits, gas wells, sulfur springsand from decaying organic matter containing sulfur. Controllingemissions of this gas, particularly from municipal sewage treatmentplants, has long been considered desirable. More recently, protectingelectronic apparatus from the corrosive fumes of these compounds hasbecome increasingly important. Furthermore, H₂S is flammable.

Ammonia (“NH₃”) is also a colorless gas. It possesses a distinctive,pungent odor and is a corrosive, alkaline gas. The gas is produced inanimal rooms and nurseries, and its control also has long beenconsidered important.

Formaldehyde (“OCH₂”) is a colorless gas with a pungent, suffocatingodor. It is present in morgues and anatomy laboratories, and because itis intensely irritating to mucous membranes, its control is necessary.

Attempts have been made to provide solid filtration media for removingthe undesirable compounds described above from fluid, or moving,streams, such as gas or vapor streams. Although a variety of impregnatedsubstrates are known for removing undesirable contaminants from fluidstreams, these known impregnated substrates are highly selective, thatis, each impregnate can treat only a specific type of compound. Inapplications where several undesirable compounds are present, the airfiltration media would either need to have several impregnates includedtherein or several different air filtration media would need to be used.This results in the currently available media not meeting the needs ofvarious industries.

The residential air quality industry has incorporated an absorbentcomposition containing two or more absorbent compounds into carpet andwindow blinds. This absorbent composition attempts to absorb numerousundesirable gaseous compounds that are present in household air,including formaldehyde (from plywood and furniture), organic solvents(from paint, adhesives and wallpaper), gases from insecticides,germicides, agricultural chemicals, and odors from cigarette smoke andpets. This absorbent composition has not, however, been applied toindustrial, commercial or residential air filtration media.

Therefore, what is needed is an air filtration media having impregnatedthereon a composition capable of absorbing multiple categories ofundesirable gases, including hydrogen sulfide, formaldehyde and ammonia.

SUMMARY OF THE INVENTION

A solid air filtration medium includes an impregnate, wherein theimpregnate contains an organic amine and an inorganic metal salt. Themedium contains from about 0.1 to about 25% by weight of impregnate.

The impregnate contains from about 0.1 to about 5% by weight organicamine, which is preferably aqueous urea, solid urea, melamine ormixtures thereof.

The impregnate contains from about 0.1 to about 5% by weight metal salt,which is preferably magnesium oxide, calcium oxide or mixtures thereof.

The impregnate optionally further includes from about 0.1 to about 10%by weight surfactant, which is preferably polyacrylic acid.

Methods for forming a solid air filtration medium include applying animpregnate to a porous substrate, wherein the impregnate includes anorganic amine and an inorganic metal salt. The porous substrate ispreferably activated alumina, silica gel, zeolite, kaolin, adsorbentclay, activated bauxite, activated carbon or combinations thereof.

Methods for removing at least two contaminants from a fluid streaminclude filtering the fluid stream with an air filtration mediumcomprising an organic amine and an inorganic metal salt.

DETAILED DESCRIPTION OF THE INVENTION

Dry scrubbing air filtration media and methods of treating a fluidstream with the media are provided. The solid filtration media can beused to remove or reduce undesirable compounds, or contaminants, from agaseous fluid stream. The solid filtration media contain an organicamine and an inorganic metal salt. The organic amine and inorganic metalsalt are preferably, but do not have to be, applied to the airfiltration media as a liquid impregnate solution. An optional surfactantis added to the liquid impregnate solution to maintain the metal saltsuspended in the solution.

Generally described, the filtration media contain a substrateimpregnated with a solution containing an organic amine and an inorganicmetal salt. The filtration media include approximately 0.1 to about 25%by weight of the solution.

The organic amine is preferably selected from aqueous urea, solid urea,melamine and mixtures thereof. The solution preferably contains fromabout 0.1 to about 5% by weight organic amine.

The metal salt is preferably selected from metal oxides such as, but notlimited to, magnesium oxide and calcium oxides. The liquid preferablycontains from about 0.1 to about 5% by weight metal salt.

When applied to the filtration media, the organic amine and metal saltallow the media to remove or reduce undesirable compounds, orcontaminants, from a gaseous fluid stream. In particular, the filtrationmedia can remove a combination of undesirable compounds, such ashydrogen sulfide, formaldehyde and ammonia. Previously known airfiltration media have been unable to effectively simultaneously filterthis wide range of compounds.

The organic amine component of the filtration media reacts withformaldehyde according to formula (I):R—NH₂+OCH₂→R—N═CH₂+H₂O  (I)

The gaseous formaldehyde is thus converted to a solid organic nitrogencompound.

The metal salt also neutralizes the formaldehyde by catalyzing thebreakdown of formaldehyde into water and carbon dioxide. The metal saltis not consumed in the catalytic reaction and is available to treatadditional undesirable compounds.

Undesirable compounds and contaminants such as ammonia and hydrogensulfide are neutralized by a catalytic reaction with the metal salt toform water and a nitrogen oxide or sulfur oxide, respectively. As withthe catalytic reaction of the metal salt with formaldehyde, the metalsalt is not consumed in the ammonia and hydrogen sulfide neutralizationreactions.

The porous substrate to which the impregnate solution is applied may beselected from the group consisting of, but not limited to, activatedalumina (Al₂O₃) (UOP Chemical, Baton Rouge, La.), silica gels (J. M.Huber, Chemical Division, Havre De Grace, Md.), zeolites (Steel HeadSpecialty Minerals, Spokane, Wash.), kaolin (Englehard Corp., Edison,N.J.), adsorbent clays (Englehard Corp., Edison, N.J.), activatedbauxite, activated carbon such as activated carbon cloth, woven or nonwoven particulate filters or combinations thereof. Preferably, theconcentration of impregnate in the filtration media is about 0.1 toabout 25% by weight.

Preferred porous substrates include alumina, activated carbon, andcombinations thereof.

Another preferred porous substrate is a combination of alumina and azeolite. Though not intending to be bound by this statement, it isbelieved that zeolites further control the moisture content of thefiltration media by attracting and holding water, which functions tokeep more of the impregnate in solution. This effect, in turn, isbelieved to improve the capacity and efficiency of the filtration media.As used herein, the term zeolite includes natural silicate zeolites,synthetic materials and phosphate minerals that have a zeolite-likestructure. Examples of zeolites that can be used in this media include,but are not limited to, amicite (hydrated potassium sodium aluminumsilicate), analcime (hydrated sodium aluminum silicate), pollucite(hydrated cesium sodium aluminum silicate), boggsite (hydrated calciumsodium aluminum silicate), chabazite (hydrated calcium aluminumsilicate), edingtonite (hydrated barium calcium aluminum silicate),faujasite (hydrated sodium calcium magnesium aluminum silicate),ferrierite (hydrated sodium potassium magnesium calcium aluminumsilicate), gobbinsite (hydrated sodium potassium calcium aluminumsilicate), harmotome (hydrated barium potassium aluminum silicate),phillipsite (hydrated potassium sodium calcium aluminum silicate),clinoptilolite (hydrated sodium potassium calcium aluminum silicate),mordenite (hydrated sodium potassium calcium aluminum silicate),mesolite (hydrated sodium calcium aluminum silicate), natrolite(hydrated sodium aluminum silicate), amicite (hydrated potassium sodiumaluminum silicate), garronite (hydrated calcium aluminum silicate),perlialite (hydrated potassium sodium calcium strontium aluminumsilicate), barrerite (hydrated sodium potassium calcium aluminumsilicate), stilbite (hydrated sodium calcium aluminum silicate),thomsonite (hydrated sodium calcium aluminum silicate), and the like.Zeolites have many related phosphate and silicate minerals withcage-like framework structures or with similar properties as zeolites,which may also be used in place of, or along with, zeolites. Thesezeolite-like minerals include minerals such as kehoeite, pahasapaite,tiptopite, hsianghualite, lovdarite, viseite, partheite, prehnite,roggianite, apophyllite, gyrolite, maricopaite, okenite, tacharanite,tobermorite, and the like.

Terms such as “filtration media”, “adsorbent composition,” “chemisorbentcomposition,” and “impregnated substrate” are all interchangeable, anddenote a substance that is capable of reducing or eliminating thepresence of unwanted contaminants in fluid streams by the contact ofsuch a substance with the fluid stream. It is to be understood that theterm “fluid” is defined as a liquid or gas capable of flowing, or movingin a particular direction, and includes gaseous, aqueous, organiccontaining, and inorganic containing fluids.

The porous substrate can also be a woven or nonwoven material such asglass fiber, crêpe paper, Kraft paper, wool, steel wool, silk,cellulosic fiber fabrics, synthetic fiber fabrics or combinationsthereof. Preferred cellulosic fiber fabrics include cotton, linen,viscose and rayon. Preferred synthetic fiber fabrics include nylon,rayon, polyester, polyethylene, polypropylene, polyvinyl alcohol,acrylics, acetates, polyamide and carbon fiber.

As discussed above, the impregnate could be, but does not have to be,applied to the filtration media as a liquid impregnate solution. Theliquid solution could be sprayed onto the filtration media or could beapplied by other known methods.

Alternatively, the impregnate could be provided as a powder. The powdercould be applied directly to the filtration media, or water or anotherliquid could be added to the powder to hydrate it prior to applicationof the impregnate composition onto the filtration media.

In addition, for extruded or pelletized filtration media (such asactivated alumina or activated carbon-based media), the powder to couldbe added directly to the alumina/carbon/etc. material prior to itsextrusion or pelletization. The impregnate would thus be more or lessevenly distributed throughout the media, in contrast to media which hashad a liquid impregnate sprayed onto its outer surfaces.

In a liquid form, or as a powder form intended to by rehydrated into aliquid prior to application to the media, the impregnate compositionpreferably contains a surfactant such as polyacrylic acid or othercompound in an amount sufficient to keep the metal salt suspended in theliquid solution prior to application to the filtration media. The amountof surfactant can be selected according to methods known by a person ofordinary skill in the art, and is typically from about 0.1 to about 10%by weight of the liquid solution.

Specific methods of applying liquid or powder impregnate compositionsonto air filtration media are known and are not important to theinvention described herein.

Contaminant Removal Methods

Also provided is a method of treating a contaminated fluid stream usingthe dry scrubbing filtration media described herein. This methodinvolves contacting the contaminated fluid stream with the solidfiltration composition provided herein. Typically, the undesiredcontaminants will be removed from air, especially from air admixed witheffluent gas streams resulting from municipal waste treatmentfacilities, paper mills, petrochemical refining plants, morgues,hospitals, anatomy laboratories, hotel facilities, museums, archives,computer and data storage rooms, and other commercial and industrialfacilities. The filtration media could also be used in residentialapplications. A liquid or powder impregnate could be sold to a consumerfor manual application to a filter by the consumer. Methods of treatinggaseous or other fluid streams are well known in the art. Any methodknown in the art of treating fluid streams with the media describedherein may be used.

Example

Air filtration media containing the impregnate solutions describedherein have been shown to be much more efficient at removing gaseouscontaminants such as hydrogen sulfide, ammonia and formaldehyde. Ascompared against a known sodium permanganate-based filtration media, forexample, the filtration media described herein has shown the followingimproved filtration capabilities:

Filtration capacity of Filtration capacity of organic amine/metal sodiumpermanganate- salt-based filtration Contaminant based filtration mediamedia Hydrogen 14%  30%  sulfide Ammonia 0% 1% Formaldehyde 2% 4%

The filtration capacity was determined according to the principlesdescribed in ASTM D6646-01, “Standard Test Method for Determination ofthe Accelerated Hydrogen Sulfide Breakthrough Capacity of Granular andPelletized Activated Carbon.” This test method is directed at filtrationof hydrogen sulfide, but was adapted for ammonia and formaldehyde.

It should be understood, of course, that the foregoing relates only tocertain embodiments of the present invention and that numerousmodifications or alterations may be made therein without departing fromthe spirit and the scope of the invention. All of the publications orpatents mentioned herein are hereby incorporated by reference in theirentireties.

I claim:
 1. A method for removing a contaminant from a fluid streamcomprising filtering the fluid stream with a filtration medium, whereinthe filtration medium comprises an impregnate comprising an organicamine and an inorganic metal salt, and wherein the inorganic metal saltcomprises magnesium oxide, calcium oxide or combinations thereof.
 2. Themethod of claim 1, wherein the contaminant is selected from the groupconsisting of hydrogen sulfide, formaldehyde, ammonia and combinationsthereof.
 3. The method of claim 1, wherein the method comprises removingat least two contaminants from the fluid stream.
 4. The method of claim3, wherein the at least two contaminants are selected from the groupconsisting of hydrogen sulfide, formaldehyde, ammonia and combinationsthereof.
 5. The method of claim 1, wherein the medium comprises fromabout 0.1 to about 25% by weight of impregnate.
 6. The method of claim1, wherein the organic amine comprises aqueous urea, solid urea,melamine or mixtures thereof.
 7. The method of claim 1, wherein theimpregnate comprises from about 0.1 to about 5% by weight organic amine.8. The method of claim 1, wherein the impregnate comprises from about0.1 to about 5% by weight metal salt.
 9. The method of claim 1, whereinthe impregnate further comprises a surfactant.
 10. The method of claim9, wherein the impregnate comprises from about 0.1 to about 10% byweight surfactant.
 11. The method of claim 9, wherein the surfactant ispolyacrylic acid.
 12. The method of claim 1, wherein the filtrationmedium further comprises a porous substrate.
 13. The method of claim 12,wherein the porous substrate is selected from the group consisting ofactivated alumina, silica gel, zeolite, kaolin, adsorbent clay,activated bauxite, activated carbon and combinations thereof.
 14. Themethod of claim 13, wherein the porous substrate is activated alumina,activated carbon, or a combination thereof.
 15. The method of claim 13,wherein the porous substrate is activated alumina, zeolite or acombination thereof.
 16. The method of claim 12, wherein the filtrationmedium is formed by applying the impregnate to the porous substrate. 17.The method of claim 16, wherein the impregnate is applied to the poroussubstrate in the form of a liquid solution.
 18. The method of claim 16,wherein the impregnate is sprayed onto the porous substrate.
 19. Themethod of claim 16, wherein the impregnate is applied to the poroussubstrate in the form of a powder.
 20. The method of claim 16, whereinthe impregnate is incorporated into the porous substrate prior toextrusion or pelletization of the substrate.
 21. The method of claim 12,wherein the porous substrate is a woven or nonwoven material selectedfrom the group consisting of glass fiber, crêpe paper, kraft paper,wool, steel wool, silk, cellulosic fiber fabrics, synthetic fiberfabrics and combinations thereof.